Xenon flash lamp for laser pumping in liquid nitrogen

ABSTRACT

This disclosure is directed to a laser system including therein a flashlamp which is operable at a temperature of about - 180* C. and lower. The laser lamp may be immersed in the coolant fluid and optically coupled to the laser element which may be contained within the coolant.

United States Patent Inventors James W. Tucker Alexandria; James N.Bradford, Falls Church, Va. Appl. No, 840,561 Filed Mar. 14, 1969Division of Ser. No. 442,838, Mar. 25. I965, Patent No. 3,449,615.Patented Mar. 9, 1971 Assignee The United States of America asrepresented by the Secretary of the Navy XENON FLASH LAMP FOR LASERPUMPING IN LIQUID NITROGEN 4 Claims, 2 Drawing Figs.

US. Cl 331/945 Int. Cl H0ls 3/04 501 Field ofSearch 331/945 56]References Cited UNlTED STATES PATENTS 3,356,966 12/1967 Miller 331/9453,449,615 6/1969 Tuckeretal 331/94.5x

Primary Examiner-R0nald L. Wibert Assistant ExaminerR. J. WebsterAttorneys--R. S. Sciascia, A. L. Branning and M. L. Crane ABSTRACT: Thisdisclosure is directed to a laser system including therein a flashlampwhich is operable at a temperature of about i 80 C. and lower. The laserlamp may be immersed in the coolant fluid and optically coupled to thelaser element which may be contained within the coolant.

Patented March 9, 1971 FIG. '2

INVENTURS JA ME 5 /V. BRA DFORD JAMES W TUCKER BY AGENT ATTORNEY XENONFLASH LAMP FOR LASER PUMPING IN LIQUID NITROGEN This is a division ofapplication serial No 442.838 filed Mar. 25, 1965. now Patent No.3,449.6l

STATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor The present invention is directed to a flashlampsuch as used in laser systems and more particularly to a flashlampuseable in a laser system operable at a temperature which is lower thanthe temperature at which the gaseous filling within the lamp freezes orat which the partial pressure of the gaseous filling is too low topermit the establishment of an electrical discharge.

I-Ieretofore suitable flashlamps have been provided for laser systemswhich are operable at room temperature. Many experiments in laserphysics and laser system application require that the laser material becooled to a temperature of negative 180 C. or lower. In a typical systemthe cooling is accomplished by immersing the laser rod in liquidnitrogen contained in a fused silica Dewar flask. The Dewar flask isplaced within the coil of a helical flashlamp, or one or more linearflashlamps are placed alongside the Dewar flask outside the liquidnitrogen. Such laser systems are operable; however, there are severaldisadvantages in such a system. For example, the dimensional constraintsof the Dewar limit the size of the laser elements that may be used, andmaximum pump-laser coupling efficiency cannot be obtained through theDewar container. Pump-laser coupling efficiency can be improved byimmersion of the flashtube in the liquid nitrogen. However, when priorart flashlamps such as xenon are immersed in a coolant at a temperaturebelow 180 C. in liquid nitrogen, the xenon gas they contain freezes orthe partial pressure becomes so low that the flashlamps becomeinoperable. Thus, the flashlamps in prior art systems must be placedoutside the Dewar flask.

The disadvantages of the prior art flashlamp-laser systems are overcomeby the present invention wherein a flashlamp is provided which can beimmersed within the coolant and thereafter operated as desired in alaser system.

It is therefore an object of the present invention to provide aflashlamp-laser system in which the flashlamp is operable at temperatureof -l 80 C. and lower.

Another object is to provide an improved flashlamp which is operable attemperatures of 180 C. and lower for any desired purpose.

Still another object is to provide flashlamps, operable at temperaturesof -180 C. and lower which use the designs, structures and components ofprior art flashlamps with only small additional cost.

Other objects, advantages and features of the present invention shouldbecome apparent from the following detailed description which is takenin conjunction with the accompanying drawing, in which:

FIG. 1, represents a linear flashlamp made in accordance with thepresent invention;

FIG. 2, represents a laser system operable at liquid nitrogentemperature with flashlamps of the present invention.

The present invention is directed to a gas-type flashlamp which may beoperated while immersed in a coolant at a temperature of l80 C. orlower. The flashlamp contains a mixture of xenon, at a partial pressureof 5 to 1,500 Torr, and one of the following gases, namely helium, neon,argon, krypton, hydrogen, or nitrogen, as a starting gas, at a partialpressure of 5 to 400 Torr. The pressures of each gas are specified for atemperature of about 25 C. The starting gas will be characterized at anyselected operating temperature by a vapor pressure high enough to allowan electrical arc discharge to be initiated. Since xenon is frozen andhas a very low vapor pressure at a temperature of l80 C., flashlampscontaining only xenon cannot-be operated at that temperature. Theaddition of a starting gas allows one to start a discharge that willheat and vaporize the frozen xenon, which will then sustain an arcdischarge Now, referring to the drawings, wherein like referencecharacters represent like parts throughout the specification, FIG. 1represents a specific embodiment of a linear flashlamp 9 made inaccordance with the teaching of the present invention. As shown, a shortthin cylindrical light-transparent envelope 10 has axially alignedelectrodes 11 and 12 positioned at opposite ends. The envelope is filledwith a mixture of argon and xenon gas in which the partial pressure ofthe argon at about 25 C. is less Torr and the partial pressure of thexenon at about 25 C. is 600 Torr. A trigger wire 13 may be placed aroundthe lamp envelope between the end electrodes for the purposes ofionizing the argon to initiate the discharge or means separate from theenvelope may be used.

FIG. 2 is a diagrammatic representation of a laser system in which oneor more flashlamps 9 made in accordance with the present inventionprovide excitation light for a laser element 14. The flashlamps 9 andlaser element 14 are immersed in liquid nitrogen 15 or any other coolantcontained in a Dewar 16 or any other suitable container. The upper endof the container is provided with a movable cover 17 which includes anoptical window 18 in axial alignment with the container. The removablecover permits one to insert into the container of liquid nitrogenflashlamp-laser assemblies having components of various types, sizes andshapes to carry out any desired operation. The window in the removablecover permits light from the laser to exit from the container. If it isdesired to have the light emerge from each end of the laser element, awindow may also be placed at the bottom of the container in alignmentwith the laser element. The container may be provided with one or morefill pipes 21 which may used to replenish the liquid nitrogen andthrough which necessary electrical conductors may be passed and securedto the flashlamp and trigger wires. However, the electrical conductorsmay be permanently retained by mechanical supports or a seal at theaperture through which they pass.

In operation, an electric potential of typically 3,000 volts ismaintained between the ends of the series of flashlamps 9 by a chargedcapacitance of typically 500 microfarads. A brief pulse of typicallyvolts 20,000 volts applied to the trigger wire initiates ionization ofthe argon in the flashlamps, causing an electrical discharge to begin,supported by the charged capacitance. That discharge due to ionizationof the argon heats and vaporizes frozen xenon in the lamps. As itvaporizes, the xenon becomes ionized by the existing discharge andallows the discharge current rapidly to reach the arc stage, whichpersists until the charge is removed from the capacitance. Light isgenerated by the arc discharge just as in prior art lamps at roomtemperature. However, the lamps 9 of this invention are immersed in theliquid nitrogen alongside the laser element 14 where the greatestproportion of the light output of the flashlamp may be transferred tothe laser element. It is clear that optical coupling means, such ascylindrical lenses between the flashlamps and the laser element, may beemployed to improve the transfer of light to the laser element. However,the lamp is immersed within the liquid nitrogen within the Dewar.

Thus, it can be seen that the introduction of argon into prior art xenonflashlamps provides suitable flashlamps for operation at lowtemperature, e.g. in the liquid nitrogen range. The present inventionhas been described for use in a linear-type flashlamp with argonstarting gas. However, the invention may be carried out in helical,annular or otherwise-shaped lamps as well and with other starting gases,such as helium, neon, krypton, hydrogen, and nitrogen; it is not to belimited to linear flashlamps with argon starting gas. Also the teachingextends to the operation of flashlamps at temperatures at which the arcsustaining operating gas freezes or at which the partial pressure of theoperatingg'as, due to the coolant, is too low to initiate an arc.

Obviously many modifications and variations of the present invention arepossible in the light of the above explanations. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A laser system operable at an ambient temperature of approximately-180 C. and lower comprising:

a container for maintaining coolant from approximately 1 80 C. andlower,

a supply of light-transmissive coolant within said container,

said coolant having a temperature of -1 80 C. and lower,

a laser element,

at least one flashlamp optically coupled to said laser element,

said laser element and said flashlamp each immersed within said coolantand operable therein.

2. A laser system as claimed in claim 1 wherein:

said system includes more than one flashlamp optically coupled to saidlaser element and operable, in said coolant.

3. A laser system as claimed in claim 1 wherein:

said coolant has a temperature of liquid nitrogen.

4. A laser system as claimed in claim 3 wherein:

said flashlamp contains an admixture of xenon and argon respective at apartial pressure approximately 600 and Torr at a temperature ofapproximately 25 C. which is operable immersed in a coolant having atemperature approximately that of liquid nitrogen.

2. A laser system as claimed in claim 1 wherein: said system includesmore than one flashlamp optically coupled to said laser element andoperable, in said coolant.
 3. A laser system as claimed in claim 1wherein: said coolant has a temperature of liquid nitrogen.
 4. A lasersystem as claimed in claim 3 wherein: said flashlamp contains anadmixture of xenon and argon respective at a partial pressureapproximately 600 and 100 Torr at a temperature of approximately 25* C.which is operable immersed in a coolant having a temperatureapproximately that of liquid nitrogen.